Blast furnace power system



March 12, 1940.

J. M. AVERY BLAST FURNACE POWER SYSTEM Filed llarch 10, 1938 2 Sheets-Sheefl COMPRESSOR ENGINE.

OR /6 MOTOR INVENTOR March 12, 1940. MAVERY 2,192,885

BLAST FURNACE POWER SYSTEM Filed latch 10, 1938 2 Shets- SheetZ INVENTOR. Julian MAW-'13 ATTORNEYS Patented Mar. 12, 1940 Julian M. Avery, Greenwich, lilo", aaslpznor to Arthur ll). Little, lino, @arnbritlae, Will, a corporation of Massachusetts implication ltliarch it, tutti, Serial No. llttitlit ll? Malena.

This invention relates to the operation of blast furnaces under internal pressure substan= tially greater than atmospheric pressure, and has particular reference to the provision of means whereby power may be recovered by expansion in an engine oi the resulting high pressure lurnace output asses, without seriously atlectina the operation of blast gas blowers, compressore or the like, when the blast pressure and volume are altered.

in my copencllng application Serial No. error, filed June 12, 1936, now Patent No. 2,131,,il3l, issued September 27, 1938, there is described a m novel method of operating blast furnaces under internal pressures substantially in excess of those employed in normal practice. Normally, the pressure of gases leaving a blast furnace, i. 'e.,

the pressure in the furnace ton, usually callecl.

20 top pressure, is, as stated in the aforementioned application, merely thatresulting from back-pressure developed by the frictional resistance to the flow of the cases through pipes, conduits, stoves, gas burners and the like, and.

it is well known that the top pressures thus developed are ordinarily less than about onefourth atmosphere gauge. In the proposed method of pressure operation, the internal pres sure, and consequently the top pressure, is in-- creased by controlling the back pressure on the gases leaving the furnace, hereinafter called the furnace cases, by any convenient means such as a throttle or expansion valve, or expansion engine. As the top pressure is thus increased, it

will be obvious that to maintain a given blast rate the blast pressure must also be increased, which requires additional blast power for a given blast rate. However, as the top pressure is in l creased, it will be evident that at some pressure,

the exact value of which will depend upon local conditions, it becomes economically advantageous to recover powerirom the furnace gases by ex paneling them through a suitable engine, which may be an expansion engine or an internal com bustlon engine, or the like.

As pointed out in the aforementioned copending application, the volume of furnace cases is a1- ways greater than the blast volume, because 'each molecule of oxygen in the blast is converted by combustion in the tuyere zone into two volumes of carbon monoxide:

(oil. with) the resultant increase in vole bolus achrommately in the ratio or about 20%. This minimum increase in volume is further considerably augmented by the volatile matter oi the carbonaceous i'uel charged, by decomposition of moisture in the blast, by direct oxidation of carbon to carbon monoxide by the oxygen contained in the charge, by carbon iiioxide evolved from the limestone in the charge, and by water vapor driven oil in olrylna: the charge, a considerable portion of which, toaether with the blast moisture, usually reacts with car 15 ban to form hydroeen and carbon monoxide. Thus, while the minimum increase in volume of furnace gases as compared with blast volume is about 20%, the increase may be and usually is very much greater, i. e., on the order oi lil%, depending upon conditions of operation.

Within economical ranges of oneratiris pres-- sure, when handling reasonably large volumes oi gas at suitable initial temperatures, modern'expension engines, as for example, gas turbines show eiifiiciencies on the order of 210%. It follows that ii the extra blast newer required to compress the blast for pressure operation, as compared with that required i'or normal operation, is ii, the amount of power recoverable by expanding the furnace gases at suitable initial temperature and with reasonably high initial pressure, is on the order oi Ax l.t0 il.-lii=ll.9il, or approximately the amount of extra blast power required. a matter of fact, the ratio of recoverable power to blast power is somewhat greater than this much calculation would indicate, because, as pointed out in said potent, as the too pressure is increased the pressure drop through the fur" uses for a given blast rate decreases, so that a part of the normal blast power which is ordi narily absorbed by frictional resistance, and is thus entirely wasted, becomes available for recovery by expansion in the manner mentioned. It will thus be evident that as top pressure and a the blast pressure are increased, the extra power required to compress the blast increases as compared with normal operation, while the power Pill iii)

recoverable from the furnace gases increases roughly in like quantity; and conversely. In accordance with the present invention, ailvantage is. taken of the condition oi? increased potential energy in the furnace cases as the result of operation at a top pressure in excess of about one-fourth atmosphere sauce, by floating' an across the blast gas line and the furnace gas line a blast gas compressor, hereinafter called a booster, and an expansion engine respectively, the two machines being mechanically or electrically linked together so that the power recovered by expanding the furnace gases in the engine is employed in whole or in part, either to boost the initial blast gas pressure to the desired blast pressure, or to compress the blast gas to some desired initial pressure, in which case the final blast pressure may be obtained by means of a separate aumliary booster. In either case, one or both of the blast gas compressors or blowers may be and is preferably equipped with other driving means, such as an electric motor, in order to provide control of the blast gas pressure without necessarily relying upon the power recovered from the furnace gases.

In. carrying out the invention I prefer to compress the blast gas to an initial pressure on the order of from /2-to 1V2 atmospheres gauge, as in normal furnace practice, by means of a compressor of conventional type. This makes possible the useful employment of present blowing equipment on a furnace converted for pressure operation, and at the same time facilitates operation under normal conditions if for any reason pressure operation is discontinued, or the pressure is temporarily sharply decreased, as, for example, during' the tapping period. When using this preferred system of operation, the additional blast gas pressure is developed by a booster, preferably of the centrifugal type, and this booster may be alternatively connectible to an expansion engine of the turbine type driven by the furnace gases, and to an auxiliary engine or electric motor. By controlling the discharge pressures of the compressor and blower, either automatically or by hand, it is then possible to distribute the total work of blast gas compression between the compressor and the booster, so that the booster uses to maximum advantage all of the power delive'red by the expansion engine, while variations in the total blast power required. not automatically compensated by the action of the expansion engine, are taken care of by variations in the power consumed by the initial compressor.

For a more complete understanding of the invention, reference may be had to the accompanying drawings, in which Figure 1 illustrates diagrammatically a preferred arrangement of the present invention, whereby the potential powers: the furnace gases produced by a blast furna a operated under pressure may in large part be ;e co vered and. employed to maximum advantage;

I Figure 2 is a diagrammatic showing of a pressure actuated control mechanism for a compress'or motor; and I Figure 3 is a diagrammatic showing of a modifled form of pressure-actuated control mechanism.

In the drawings, numeral l designates a blast furnace of more or less conventional design and construction, but modified in the manner described in the aforementioned patent to operate under a top pressure in excess of about onefourth atmosphere gauge. 80 modified, the furpressure look so as to equalize the pressure between the iurnace ill and the lock ii during charging operations, whereby the lower bell may be readily lowered without the additional force which would otherwise be required to lower it against the furnace pressure.

The bustle pipe it supplying the tuyres i! may be also of conventional construction and supplied with blast air or other gas by the blast feed duct it connected to the compressor It, with or without an auxiliary booster it between the compressor it and the bustle pipe it, depending upon pressure and other operating requirements. Preferably such an auxiliary booster H is provided and may be of the centrifugal type. Both the blast gas compressor i 5 and the booster I! may be provided with auxiliary driving engines or motors it and it, respectively, connectible and disconnectible at will by means of respective clutches 2d and it.

The furnace gases, issuing from the furnace top through down-take duct 22, are led through a conventional dust catcher Z3 and scrubber at or the like, for removing the entrained dust and foreign material, so that the gases may be directly employed for operating the expansion engine 25, which may be a reciprocating engine or a turbine, depending upon requirements. The expansion engine 25 thus replaces internal combustion engines or the like customarily supplied with furnace gas cleaned in any conventional manner, and at the same time performs the function of creating a back pressure on the furnace gases and thus building up pressure within the furnace it to the desired amount for pressure operation.

The expansion engine 25 may be connected through a differential 29, gearing El and clutch 28 to the compressor it and through a differential 2t, gearing 2t and clutch 39 to the booster i1. It will be understood that as clutches 28 and 3B are disengaged the corresponding side of the differential 2b is locked, either by locking the clutch or otherwise, and that when clutches 28 and lit are engaged the respective clutches and ii are disengagedand vice versa. Alternatively, engine 26 may be an internal combustion engine, whose developed power will inherently vary with the initial pressure and thus the engine automatically develops more or less blast power as required. In either case, instead of direct mechanical connection between the engine and the compressor it and/or the booster ii, the engine 25 may be used to drive an electric generator, and the compressor it and/or booster ll driven by electric motor or motors actuated by the generator or by other source of electric power.

In operation, the compressor it may, for example, be driven by an engine or motor I 8 with clutch 28 disengaged as shown. Compressor it then may compress the blast air or other gas to an initial pressure on the order of to 1 atmospheres gauge, as in normal furnace practice. The expansion engine 25, or the equivalent internal combustion engine, by its resistance to motion, develops the requisite back pressure ,on

I the furnace gases to create the desired internal pressure within the furnace It, as described, requiring increasing blast pressure as the back pressure develops through the system and increases to the desired degree. The booster i! may accordingly be placed into operation by connecting it through clutch 2| to its auxiliary motor i8, clutch 30 being disengaged. As the exlid till

t in" mam pension engine 25 develops power under operation by the furnace gases, the booster may then be disconnected from the auxiliary engine or motor N by disengaging clutch II, and connected to the expansion engine 25 by engaging clutch 30, so that the requisite pressure of the blast feed gas for pressure operation 01' the furnace it is ing on the furnace gases in the manner described.

Alternatively, the initial compressor engine or motor it may be adapted to provide pressure to cause'the expansion engine 26 to become effective in driving the booster ii, in which case the booster automatically develops the required additional pressure without provision of auxiliary engine or motor iii.

With such arranaements the existing blowing equipment, 1. e. the compressor it, of a blast i'urnace converted to pressure operation according to the invention of the aforementioned application, may be usefully employed. It also enables the return to normal operation or reduced blast pressure clurins, the tapping period, simply by cutting out the booster ll, which may'then be positioned in a valve controlled by-pass of the blast gas duct to in a manner readily understood. A by pass i2 may also bleed oil some of the furnace gases for blast preheating equipment or the-Elite.

Since the engine it and booster ll "float" between the iurnace gas and blast gas lines, the booster ll may supplement the compressor iii, by performing its booster function and also part of the initial compression worlr of the compressor it, at times when the power output of the expansion engine iii erceeds that necessary for operation oi the booster alone. in that case the speed or pressure control oi the compressor it) and engine or motor ill may be adjusted, such as with a throttle in the case oi an engine or with a rhcostat in the case of a motor, either manually or automatically by an electric control 3i operated in response to chances in pressure in the blast gas duct iii above and/or below a pro determined degree. Typical mechanisms responsive to pressure in the blast duct it for controlling operation of the motor in are disclosed in Figures 2: and 3. In the device disclosed in Figure the automatic control 3!] includes a diaphrasm responsive tovariation in pressure in duct it and connected to a pivctally supported arm of a rheostat which includes contacts and interposed. resistances ill. As the diaphragm is moved inwardly or outwardly in response to variation in pressure in the blast duct i i, the resistance in circuit with the electric motor ill is varied, reducing the speed of the motor it! the pressurein the duct Ii i'increases and increasing the speed oi the motor it as the pressure decreases.

if a gas engine it is used, the rheostat is connected in circuit with a solenoid lit which controls a throttle valve in the fuel line oi the engineas illustrated in Figure 3. In this device as the pressure in the duct it increases the resistance oi the rheostat is decreased so that the throttle is partially or completely closed against the tension of the spring fill. As the pressure in the duct it decreases, the resistance of the rheothe power delivered by the expansion engine 25.

If desired or feasible, as previously intimated, the auxiliary motor it for booster I! may be dispensed with by providing the initial compressor it 01 sui'ilcient capacity to build up a pressure substantially in excess of its normal operating pressure, and if this method is followed, the discharge pressure of the initial compressor it will necessarily be varied to compensate for the pressure developed by the booster H as soon as it begins to function under operation by. engine 3!, as determined by the automatic pressure responsive control ti, for example. Thus, as the top pressure begins to increase, the power developed by the engine it and transmitted to booster ill will increase, so that the pressure developed by compressor it may be gradually decreased in order to maintain the desired blast pressure. This is the ideal method of operation of the arrangement of the invention, for variations of blast pressure and of top pressure are automatically compensated with only sliaht variations in the operating conditions or the initial compressor iii. This is especially advantageous in case it is desired to decrease the blast'pressure when slag or metal is tapped from the iurnace.

Alternatively, the furnace iii may be started and operated with the booster ll, disconnected by disengaged clutch Bil from the expansion engine as and connected by engaged clutch it to a mo tor iii, while compressor it may be connected by encased clutch to to the expansion engine and disengaged from its motor to by. disencauod clutch to. Depending upon the pressure condi-- tions required, a large capacity compressor iii may provide all or" the blast from the power turnlshed by the expansion enaine 2b, the automatic pressure-responsive cut-out or control ill recu- Eating the operation of the booster motor iii in accordance with the blast pressure requirements by adjusting the throttle or rheostat iiii". y

it will be seen that the arrangement of the present invention provides a very efiective means for recovering potential power of expansion from the iurnace gases as the result of operation oi a blast furnace under pressure in accordance with the invention of said patent. and while certain preferred arrangements of the invention have been illustrated and described herein, it is to be understood that the invention is not limited thereby, but is susceptible of chances in form and detail within the scope of the appended claims.

I claim:

1. The method of operating a sealed blast lurnace, which comprises supplying the blast feed gas at superatmosphcldc pressure by means of a compressor, maintaining the furnace under superatmospheric top pressure in excess of about one-fourth atmosphere gauge, operating a pressure-responsive engine with the furnace discharge gases, and utilizing the power output of said engine to aid in drivina said compressor.

2. The method of operating a sealed blast furnace, which comprises supplying the blast feed gas at superatmospheric pressure by means of a compressor, maintaining the furnace under superatrnospheric top pressure in excess of about one-fourth atmosphere gauge, operating a combastion engine with the combustible furnace discharge gases, and utilizing the power output of furnace, which comprises supplying the blast feed hit lid

till

(lid

gas at superatmospheric pressure by means of a driven compressor, creating back pressure on the gas discharged from the furnace by means of an expansion engine to maintain a superatmospheric top pressure within the furnace in excess of about one-fourth atmosphere gauge, and utilizing the power dutput of said engine to aid in driving said compressor.

4. The method of operating a sealed blast furnace, which comprises starting the furnace by supplying the blast feed gas with a driven compressor, increasing the pressure of the blast feed plied by said engine increases.

*which comprises starting the furnace by supplying the blast feed gas at superatmospheric pressure with a primary compressor and'an auxiliary compressor, maintaining the furnace under superatmospheric top pressure in excess of about one-fourth atmosphere gauge, operating an expansion engine with the furnace discharge gases, driving said auxiliary compressor with said engine, and reducing the blast of said primary compressor as the auxiliary compressor increases the blast feed gas pressure in response to the increasing power output of said engine.

6. In a blast furnace having a blast feed pipe and a. gas discharge pipe, the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, means for compressing the blast feed gas supplied to the blast feed pipe to superatmospheric pressure, an engine connected to the gas discharge pipe for operation by the furnace discharge gases and exerting a back pressure to maintain a superatmospheric internal pressure in said furnace, and driving connections between said engine and said compressing means, said engine supplying at least part of the power required to drive-said means during operation of the furnace.

7. In a blast furnace having a blast feed pipe and a gas discharge pipe, the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, a compressor for compressing the blast feed gas supplied to the blast feed pipe, driving means for said compressor, a booster compressor between said furnace and the compressor for increasing the blast feed gas pressure, an expansion engine connected to the gas discharge pipe for operation by the furnace discharge gases, driving connections between said engine and said booster compressor, and means for decreasing the rate of operation of said compressor as the power sup- 8. In a blast furnace having a blast feed pipe and a gas discharge pipe, the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, a compressor for compressing the blast feed gas supplied to the blast feed pipe, a booster compressor between said furnace and the compressor for increasing the blast feed gas pressure, driving means therefor, an engine connected to the gas discharge pipe for operation by the furnace discharge gases, driving connections between said engine and said booster compressor, and means responsive to a predetermined degree of pressure in the blast feed pipe for disconnecting said driving means from the booster compressor, said engine, only, then driving said booster compressor.

9. In a blast furnace having ablast feed pipe and a gas discharge pipe, the combination of a sealed furnace shaft capable of operation at su-' peratmospheric pressure, a compressor for compressing the blast feed gas supplied to the blast feed pipe, a booster compressor between said furnace and the compressor for increasing the blast feed gas pressure, driving means therefor, an engine connected to the gas discharge pipe for operation by the furnace discharge gases, driving connections between said engine and said booster compressor, and means responsive to predetermined higher and lower degrees of pressure in the blast feed pipe for respectively disconnecting and reconnecting said driving means to the booster compressor, said engine supplying all of the power for drivinglsaid booster compressor when the driving means is disconnected and part of the power when the driving means is connected to the booster compressor during operation of the furnace.

-10. In a blast furnace having a blast feed pipeand a gas discharge pipe, the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, a compressor for compressing the blast feed gas supplied to the blast feed pipe to superatmospheric pressure, driving means therefor, an expansion engine connected to the gas discharge pipe for operation by the furnace discharge gases, a booster compressor connected to said blast feed pipe between said furnace and the compressor, driving connections between said engine and said booster compressor, and means for decreasing the output pressure of said compressor as the supplemental output pressure supplied by said booster compressor increases.

11. In a blast furnace having a blast feed pipe and a gas discharge pipe, the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, a compressor for compressing the blast feed gas supplied to the blast feed pipe to superatmospheric pressure, driving meanstherefor, an engine connected to the gas discharge pipe for operation by the furnace dis charge gases, a booster compressor connected to said blast feed pipe between said furnace and the compressor, driving connections between said engineand said booster compressor, and means for regulating the speed of said compressor driving means to compensate for variations in the pressure output of said booster compressor.

12. In a blast furnace having a blast feed pipe and a gas discharge pipe, the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, a compressor for com-- pressing the blast feed gas supplied to the blast feed pipe to superatmospheric pressure, driving means therefor, an engine connected to the gas discharge pipe for operation by the furnace discharge gases, a booster compressor connected to said blast feed pipe between said furnace and the compressor, driving connections between said engine and said booster compressor, and means responsive to a predetermined increased blast feed pressure for reducing the speed of said compressor driving means.

13. In a blast furnace having a blast feed pipe and a gas discharge pipe. the combination of a sealed furnace shaft capable of operation at superatmospheric pressure, a compressor for compressing the blast feed gas supplied to the blast feed pipe to superatmospheric pressure, driving means therefor, an engine connected to the gas discharge pipe for operation by the furnace discharge gases, a booster compressor connected to said blast teed pipe between said ,furnace and the compressor, operative. connections between said engine and said booster compressor, and means responsive to predetermined increased and decreased pressures in the blast feed pipe for respectively decreasing and increasing the speed of said compressor driving means.

JULIAN M. AVERY. 

